The present invention relates to a method for rotation speed control of a rotary element in the drive line of a vehicle.
The term “rotary element” means a shaft, such as a longitudinal drive shaft (for example propeller shaft) or a transverse drive shaft (that is to say wheel axle) or other power transmission element forming part of the drive line and adapted for rotation.
The term “drive line” means the entire power transmission system from the engine of the vehicle to the ground engagement elements. The drive line therefore includes clutch, gearbox (and any transfer gearbox present), propeller shaft (or propeller shafts), transverse drive shafts etc. Hydraulic, electric and other drive systems are also included within the term drive line.
The term “ground engagement elements” includes wheels, caterpillar tracks etc.
The invention can be applied to wheel-borne vehicles, track-borne vehicles and vehicles running on rails. Primarily wheel-borne vehicles are intended. The invention can also be applied to passenger cars, trucks, buses and other road vehicles but is primarily intended for cross-country vehicles, such as four-wheel drive passenger cars, and working vehicles, such as frame-steered dumpers, wheel loaders, excavators etc. The invention is particularly applicable in vehicles with a number of driven axles and will below be described for a frame-steered dumper for the purpose of exemplification.
A fundamental problem for all vehicles with drive at a number of ground contact points is how the driving power is distributed. It is desirable to control the rotation speeds of the wheels so that the slip in the longitudinal direction is the same at all ground contact points because this results in excessive slip at individual ground contact points being prevented. Slip is the standardized difference between the speed of the wheel at the ground contact point and the speed of the ground at the same point.
One way of bringing about the desired identity of longitudinal slipping would be to connect the drive of all the wheels mechanically. However, this would not work during cornering. During cornering, the ground moves at different speed at the various ground contact points. The ground under the outer wheels moves at higher speed than the ground under the inner wheels because the outer wheels have a greater distance to cover in the same time as the inner wheels. During cornering, the ground under the front wheels also moves at higher speed than the ground under the rear wheels.
The problem of distributing tractive power in an effective way during cornering as well is conventionally solved by dividing the torque in a given, fixed ratio with the aid of a differential. The rotation speed is then controlled by the speed of the ground at the various ground contact points and by the slip. However, the slip cannot be controlled. If the product of vertical load and ground friction does not correspond to the torque ratio in the differential, the slip can increase unlimitedly, the wheels slip and the total tractive power transmitted is limited by the slipping ground contact.
The problem of uncontrolled slip is usually reduced by various measures for braking the slip, for example by using what is known as a differential lock. The differential lock conventionally comprises a claw coupling which locks the differential mechanically. The disadvantage of differential locks is that the speed difference during cornering is offset as slip at the ground contact points concerned. This results in great constrained torques which shorten the life of the drive line, give rise to losses and cause great tire wear.
WO03/006846 describes a large number of different drive line solutions which afford opportunities for remedying the abovementioned problems during cornering.
It is desirable to provide a method for controlling the rotation speed of a rotary element in the drive line of a vehicle in a way which results in a longer life of the drive line and/or lower losses in the form of fuel consumption and/or tire wear.
In a method for controlling rotation speed of at least one rotary element in the drive line of a vehicle according to an aspect of the present invention, at least one operating parameter of the vehicle being detected repeatedly, the value of the detected operating parameter being used for calculating a rotation speed value corresponding to a given slip of at least one of the ground engagement elements of the vehicle at its ground contact point, which ground engagement element is driven via the rotary element, and the rotation speed of the rotary element being controlled on the basis of the calculated rotation speed value. Control is preferably carried out automatically and continuously during operation. The rotation speed of the rotary element is preferably controlled so that the slip is minimal at the ground contact point. This method affords opportunities for the driving power from the engine to be transmitted to the ground with the smallest possible power loss.
According to a preferred embodiment, said operating parameter comprises the steering angle of the vehicle. The steering angle indicates whether the vehicle is being driven in a bend, and the slip is regulated corresponding to the cornering.
According to a preferred embodiment, the rotation speed of the rotary element is controlled so that the slip is essentially the same at least two of the ground engagement elements of the vehicle. The rotation speed of the rotary elements is preferably controlled so that the slip is minimal at the ground contact points. This makes it possible to obtain optimum grip against the surface for good propulsion.
According to another preferred embodiment, a reference rotation speed is determined for a part of the drive line which is on the opposite side of said rotary element in relation to the ground engagement element driven by it, and control of the rotation speed is carried out in relation to this reference rotation speed. The reference rotation speed is preferably determined on the basis of conditions on the input side of the rotary element, that is to say before the regulation. At least one rotation speed of a rotary element in said drive line part is preferably detected, and this detected rotation speed is used as said reference rotation speed.
According to another preferred embodiment, a value for a rotation speed increase for the rotary element is calculated, and the rotation speed of the rotary element is controlled corresponding to the rotation speed increase. The rotation speed increase dw is preferably calculated according to dw/w=(R1/R2)*(r2/r1)−1, where
w is the reference rotation speed,
R1 and R2 are different curve radii and
r1 and r2 are different rolling radii.
According to a preferred embodiment, the rotation speed of the rotary element is controlled so that free rotation of said ground engagement element is counteracted and a torque delivered to said ground engagement element is allowed to vary.
Further preferred embodiment and advantages thereof emerge from the description below, the figures and the claims.